// #include<bits/stdc++.h>
#include <iostream>
#include <vector>

using namespace std;

int main() {
	int n, k;
	cin >> n >> k;

	long result = 0;
	for (int i = 1; i <= n; i++) {
		result += k*i;
	}
	cout << result;
	return 0;
}